1. Field of the Invention
The present invention relates to a thin film single crystal diamond substrate. More particularly, it relates to a substrate which comprises a thin film of epitaxially grown single crystal and is useful for a diamond base semiconductor device.
2. Description of the Prior Art
A semiconductive material for use in the production of a semiconductor device should be in the form of highly pure single crystal or of a layer of highly pure single crystal. In the production of a currently widely used planar type semiconductor devices, the formation of a thin film of a single crystal is an essential step of the production.
While silicon is conventionally used as a semiconductive material, application of diamond for a heat resistant semiconductor, a high power transistor and the like has been sought since the diamond has unique characteristics as a semiconductive material.
At present, only a single crystal diamond is industrially produced by an extra-high pressure apparatus, and a substrate made from such synthetic diamond particle has at most an area of several millimeter square. Therefore, the conventional single crystal diamond substrate cannot be used when a substrate having a large area is required for producing a large current device or when an integrated circuit is produced by microprocessing with a stepper. In addition, the high cost of the synthetic diamond prevents its wide use in the mass production of semiconductor.
Recently, a chemical vapor deposition (CVD) method has been developed, in which a mixed gas of, for example, methane and hydrogen is excited and reacted by microwave plasma or heating and a diamond thin film is deposited on a base plate, and a single crystal diamond film is epitaxially grown on a single crystal diamond substrate (Fujimori et al, Vacuum, 36, 99-102 (1986) the disclosure of which is hereby incorporated by reference).
However, by the CVD method, a polycrystal diamond film is formed on a silicon or gallium-arsenide (GaAs) substrate, and a single crystal diamond film can be formed only on the single crystal diamond substrate having a small area. Thus, it is desired to provide a thin film single crystal diamond substrate which is economically produced and has a large area.